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Engineering endochondral ossification using Sonic Hedgehog for bone regeneration

ABSTRACT: Endochondral ossification (EO) is the natural route for the regeneration of large and mechanically challenged bone defects. Regeneration occurs via a fibrocartilagenous phase which turns into bone upon vascularization and the formation of a transient collagen type X extra cellular matrix. These two critical initiator of EO are mediated by Hedgehog proteins. We investigated a tissue engineering approach using Sonic Hedgehog (Shh) as a pleiotropic factor regulating the in vitro formation of a vascularized bone tissue precursor for in vivo endochondral bone formation. The tissue engineered graft was formed using human mesenchymal stem cells and prevascularized using human umbilical vein endothelial cells. We show that Shh induced, in vitro, the maturation of the engineered vascular network along with the expression of collagen type X which resulted, in vivo, in an improved vascularization and the rapid formation of large amounts of osteoids through EO. Osteoids further matured into, currently unmatched, clinically relevant amount of lamellar bone including osteoclasts, bone lining cells and bone marrow-like cavities. This result suggests that Hh is a master regulator of EO allowing for the formation of complex tissues with considerable therapeutic potential for bone regeneration.

ORGANISM(S): Homo sapiens

PROVIDER: GSE22293 | GEO | 2012/09/01

SECONDARY ACCESSION(S): PRJNA127409

REPOSITORIES: GEO

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Project description:Runx2 and Axin2 regulate skeletal development. We recently determined that Axin2 and Runx2 molecularly interact in differentiating osteoblasts to regulate intramembranous bone formation, but the relationship between these factors in endochondral bone formation was unresolved. To address this, we examined the effects of Axin2 deficiency on the cleidocranial dysplasia (CCD) phenotype of Runx2+/- mice, focusing on skeletal defects attributed to improper endochondral bone formation. Axin2 deficiency unexpectedly exacerbated calvarial components of the CCD phenotype in the Runx2+/- mice; the endocranial layer of the frontal suture, which develops by endochondral bone formation, failed to mineralize in the Axin2-/-:Runx2+/-mice, resulting in a cartilaginous, fibrotic and larger fontanel than observed in Runx2+/- mice. Transcripts associated with cartilage development (e.g., Acan, miR140) were expressed at higher levels, whereas blood vessel morphogenesis transcripts (e.g., Slit2) were suppressed in Axin2-/-:Runx2+/-calvaria. Cartilage maturation was impaired, as primary chondrocytes from double mutant mice demonstrated delayed differentiation and produced less calcified matrix in vitro. The genetic dominance of Runx2 was also reflected during endochondral fracture repair, as both Runx2+/- and double mutant Axin2-/-:Runx2+/- mice had enlarged fracture calluses at early stages of healing. However, by the end stages of fracture healing, double mutant animals diverged from the Runx2+/- mice, showing smaller calluses and increased torsional strength indicative of more rapid end stage bone formation as seen in the Axin2-/- mice. Taken together, our data demonstrate a dominant role for Runx2 in chondrocyte maturation, but implicate Axin2 as an important modulator of the terminal stages of endochondral bone formation. 4 mice per genotype X 4 genotypes: wildtype (WT), Runx2+/- (R-Het), Axin2-/- (A-KO), Axin2-/-:Runx2+/- (A-KO:R-Het). Total = 16 samples

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Engineering endochondral ossification using Sonic Hedgehog for bone regeneration

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